Flexible substrates such as rolled steel foil, polymides, liquid crystal polymer, or other flexible plastics have considerable advantages over rigid substrates in a variety of applications. Flexible substrates can enable or improve the production of technologies such as flexible displays, curved circuits, curved detector arrays, thin film transistors (TFT), and display backplane matrices. Liquid crystal displays (LCD) and organic light emitting diodes (OLED) built on a flexible substrate can be made to conform to any shape, making them ideal for many applications, such as for a car dashboard or eventually an electronic newspaper. Flexible substrates can be thinner, lighter, less brittle, and more rugged than the rigid substrates that presently predominate.
However, despite their many advantages, flexible substrates offer new challenges as well. One challenge is maintaining the integrity of all of the layers during and after flexing of the substrate. When a device that has been manufactured on a flexible substrate is flexed, it creates stresses on all of the device layers since the substrate may be much thicker than any applied layer. Stress can also be generated by a mismatch of thermal expansion coefficients in the materials used, or a differential change in physical size due to changes in humidity or pressure. These stresses can cause cracking in the layers, and dramatically reduce the lifespan of electronic devices. This cracking can be especially destructive to the conductors in flexible electronic devices. Cracking causes the conductors to break, which renders devices inoperative.
One method used to address the problem of broken conductors is to increase their thickness such that they will not break when the substrate is bent. However, this does not guarantee that the conductor will not break. This practice also uses significantly more metal and may increase the cost of production, lower the accuracy of line placement, increase the processing time, and create unwanted topography during processing.
To produce electronic devices on flexible substrates suitable for consumer use, new methods are needed to overcome the limitations of the current methods. Thus, there remains a need for methods of manufacturing flexible electronics that ameliorate or eliminate the problem of broken conductors.